Low Conductivity Frequency Selective Surfaces for a Fabry Perot Cavity Antenna Configuration

This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63/702,010 filed Oct. 1, 2024, the content of which is incorporated herein by reference in its entirety.

The disclosure relates to planar antennas and, in particular, to planar antennas having a frequency selective surface in a Fabry-Perot cavity type configuration.

Emerging wireless technologies, including 5G and 6G telecommunications and various sensing and imaging systems, tends to operate in the millimeter waveband and at sub-terahertz frequencies. This waveband offers greater bandwidth, thereby enabling enhanced functionality, for applications such as autonomous cars and augmented and virtual reality, amongst others. However, signal losses are also greater at these frequencies, and high gain antennas are required for communication. Conventionally, for planar antennas, gain can be enhanced using a dielectric superstrate or by designing antenna arrays. One of the effective methods recently developed is to use frequency selective surface (FSS) in a Fabry Perot cavity (FPC) type antenna configuration. FPC antenna configuration has an advantage over both arrays and dielectric superstrates as it uses simple feeding and can be designed on thin and lower dielectric constant substrates. Various configurations and topologies of FSS have been studied for gain enhancement in which FSS patterns are conventionally made of high conductive material such as copper.

6 According to a first aspect, embodiments of the disclosure relate to an antenna. The antenna comprises a substrate having a first major surface and a second major surface. A ground plane is spatially disposed a first distance from the second major surface of the substrate, and a patch array is disposed on the second major surface between the substrate and the ground plane. Patches of the patch array are comprised of a material having a conductivity of 1×10S/m or more, and the patches of the patch array are printed onto the second major surface of the substrate.

6 7 According to a second aspect, embodiments of the disclosure relate to a method of fabricating an antenna. In the method, patches of a material are deposited on a substrate to define a patch array. The substrate has a first major surface and a second major surface, and the material is deposited on the second major surface. A ground plane is arranged a first distance from the substrate such that the patch array is disposed between the substrate and the ground plane. The material of the patches comprises a conductivity in a range from 1×10S/m to 5×10S/m.

According to a third aspect, embodiments of the disclosure relate to a method of transmitting a signal having a frequency in a range from 10 GHz to 1 THz. In the method, the signal is received from a source antenna at the antenna according to the first aspect. The signal is reflected between the patch array and the ground plane, and the signal is transmitted through the first major surface of the substrate at a gain of at least 10 dBi.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.

6 7 Reference will now be made in detail to various embodiments of a Fabry-Perot cavity (FPC) type antenna in which the frequency selective surface (FSS) is formed using materials with a conductivity as low as 1×10S/m, examples of which are illustrated in the accompanying drawings. As will be discussed more fully below, the broadening of the usable materials for such FPC-type antennas allows for fabrication of the antennas using new techniques not previously available for conventional high conductivity (e.g., >1×10S/m) materials. To the inventors' knowledge, the effect of FSS conductivity on the peak gain performance of FPC antenna configuration has not previously been investigated. The inventors surprisingly and unexpected discovered that the FPC antenna can also be designed using less conductive FSS materials with minimal loss in antenna peak gain. Such a finding is contrary to other conventional planar antenna designs, such as microstrip arrays, where significant loss in peak gain results from a decrease in conductivity. In this regard, the design space for high gain antennas is greatly increased, allowing the use of relatively low conductivity and transparent materials, such as transparent conductive oxides (e.g., indium tin oxide) and glass, or the use of relatively low conductive metallic ink in printing. These and other aspects and advantages of will be described in relation to the embodiments provided below and in the drawings. These embodiments are presented by way of example and not by way of limitation.

1 FIG. 100 100 102 104 106 106 104 108 104 106 102 110 102 depicts an exemplary embodiment of an antennaaccording to the present disclosure. The antennaincludes a substratehaving a first major surfaceand a second major surface. The second major surfaceis opposite to the first major surface. A minor surfaceconnects the first majorsurface to the second major surfacearound a periphery of the substrate. A ground planeis spatially disposed a first distance D from the substrate. In one or more embodiments, the first distance D is about 0.5λ, wherein λ is the antenna operating wavelength in free space. As used herein, the term “about” encompasses values within 20%, such as within 15%, 10%, 5%, or 2.5%, of the stated value (i.e., +/−20%, such as +/−15%, +/−10%, +/−5%, or +/−2.5%).

112 106 102 110 112 100 110 114 114 116 110 100 1 FIG. 1 FIG. A patch arrayis disposed on the second major surfacebetween the substrateand the ground plane. The patch arraydefines the FSS for the operation band of the antenna. In one or more embodiments, the ground planefurther comprises a receiver or transmitter, such as a waveguide probe antenna, a waveguide slot antenna, or a microstrip or patch antenna. In the embodiment shown in, the receiver or transmitter is depicted as a waveguide probe antennahaving an openingextending through the ground plane. As would be understood by one of ordinary skill in the art, the antennadefined by the structure depicted inis of the FPC-type, which are highly directive planar antennas also providing high gain.

102 102 102 102 104 106 102 102 In one or more embodiments, the substrateis selected from a group consisting of fused silica, quartz, alumina, and FR-4, amongst other possibilities. In embodiments, the fused silica can be high-purity fused silica (HPFS). As used herein, “HPFS” is silica that contains less than 1 ppb of water (OH) measured using Fourier-transform infrared spectroscopy (FTIR) and less than 1 ppb of alkali and metal impurities measured using inductively coupled plasma mass spectrometry (ICP-MS). In one or more embodiments, the substrateis transparent such that the substrate transmits at least 70%, at least 80%, or at least 90% of light having a wavelength in a range of 380 nm to 750 nm incident on the first major surface through the second major surface. Advantageously, such transparent substratescan be used for window applications (e.g., architectural or vehicle glazing). In one or more embodiments, the substratecomprises a thickness T between the first major surfaceand the second major surface, and the thickness T is in a range of from 0.1λ to 0.6λ, such as from 0.1λ to 0.5λ, from 0.1λ to 0.4λ, from 0.2λ to 0.5λ, or from 0.2λ to 0.4λ, where λ is the antenna operating wavelength in the substrate(i.e., taking into account the dielectric properties of the substrate).

2 FIG. 2 FIG. 112 112 118 112 118 112 118 118 102 100 118 102 118 depicts an example embodiment of a patch arrayaccording to the present disclosure. In one or more embodiments, the patch arraycomprises an array of patcheshaving an array size in a range from 5×5 to 1000×1000. In one or more embodiments, the patch arraycomprises patcheshaving any of a variety of shapes, such as squares, rectangles, circles, dipoles, ellipses, triangles, disc sectors, circular rings, or ring sectors, amongst other possibilities. In the embodiment shown in, the patch arraycomprises patcheshaving a square shape. In one or more embodiments, a spacing S between adjacent patchesis about 0.1λ, where λ is the antenna operating wavelength in the substrate. In one or more embodiments, the antennais configured for use at a frequency in a range from 10 GHz to 1 THz, corresponding to operational wavelengths (λ) in free space in a range of 0.3 mm to 3 cm. In one or more embodiments, each patchcomprises a patch dimension L in a range of from 0.1λ to 0.6λ, such as from 0.1λ to 0.5λ, from 0.2λ to 0.6λ, or from 0.2λ to 0.5λ, where λ is the antenna operating wavelength in the substrate. Depending on the shape of the patch, the patch dimension L could be a side length (e.g., of a square), a radius (e.g., of a circle or disc sector), or a height (e.g., of a triangle).

118 112 118 118 118 118 6 6 8 6 7 7 Patchesof the patch arrayare comprised of a material having a conductivity as low as 1×10S/m, in particular in a range of 1×10S/m to 1×10S/m, and most particularly in a range of 1×10S/m to 1×10S/m. In one or more embodiments, the material for the patchesis selected to have a conductivity less than that of copper, in particular a conductivity of 5×10S/m or less. In one or more embodiments, the material is selected from a group consisting of a conductive metal oxide (e.g., indium tin oxide), a metallic ink, bronze, brass, aluminum, stainless steel, tin, or combinations thereof. Advantageously, expanding the range of conductivity for the patches allows for the use of materials that can be processed differently, such as using various printing techniques. For example, in one or more embodiments, the patchesare printed on the substrate using inkjet printing, aerosol jet printing, or screen printing, amongst others. In another example according to one or more embodiments, the patchesare deposited on the substrate using physical vapor deposition, sputtering, chemical vapor deposition, or electroplating, amongst other possibilities. Such deposition processes use less materials and may allow for faster processing of the patches. In contrast, conventional etching techniques require deposition of a film, application of accurate masks, and removal of the film in negative areas, potentially leading to waste. Further, conventional electroplating techniques require exact application of masks to define the desired deposition locations, and electroplating takes time to build up the desired layer thickness.

112 102 110 112 110 110 After the deposition of the patch array, the substrateis arranged at the first distance D from the ground planewith the patch arrayfacing the ground plane. As mentioned above, the ground planemay include an emitter or receiver to transmit outgoing signals or receive incoming signals.

3 FIG. 3 FIG. 118 18 118 18 106 102 118 120 118 118 118 118 106 102 18 20 118 18 118 122 18 22 118 122 120 118 depicts a comparison of a patchdeposited via a printing process according to embodiments of the present disclosure as compared to a patchformed via conventional etching or electroplating processes. As can be seen from the side view, each patch,has a maximum height H above the second major surfaceof the substrate. The printed patchhas as variable height H across the top surface as well as rounded verticesalong the edges. In one or more embodiments, the height H of the printed patchmay vary by as much as 20% (100×(maximum height−minimum height)/maximum height), in particular in a range from 5% to 20%, and most particularly in a rage from 10% to 20%, across the top surface of the printed patch. For printed patches, this results from the formation of the patchfrom droplets of the patch material that are deposited and merge on the second major surfaceof the substrateas well as the effect of solvent evaporation after deposition. By comparison, the conventional patchhas substantially sharp, angular verticesand consistent height H across the top surface. This results from the process of removing a portion of a film around a mask or depositing a film within a cavity defined by a mask. Further, as shown in the top view of the patches,, the patchdeposited by a printing process has rounded cornerswhere two linear sides meet, whereas the patchdeposited by a conventional etching or electroplating process has substantially angular cornerswhere two linear sides meet. The embodiment of the printed patchshown inis square in shape, but the rounded cornerswould be present for any polygonal shape. Further, the rounded verticesalong the vertical edge and variable height H would generally be present for any curved or linear edges defining the shape of the patch.

100 112 102 102 102 112 110 1 FIG. Having described the general structure of the antenna, an antenna according to the present disclosure was constructed. The source antenna was a waveguide probe antenna (Product No. PEWAN1124, Pasternack Enterprises, Irvine, CA, USA), such as schematically depicted in. The patch arraywas printed on a high purity fused silica (HPFS) substrate. The thickness T of the HPFS substratewas 0.5 mm, and the HPFS substratewas square with a side length of 10 mm. The patch arraywas spaced a first distance D of 1 mm from the ground plane.

100 118 102 112 118 118 112 112 112 112 2 FIG. To test the effect of the material conductivity on the performance of the antenna, square patchesof different materials were deposited on the HPFS substratein 9×9 patch arrays. Specifically, the material of the patcheswere selected to be copper, aluminum, bronze, and indium tin oxide (ITO). The dimensions of the patchesand patch arraywere optimized for maximum antenna gain in the band of 150 GHz to 170 GHz. In this regard and with reference to, the patch dimension L was 0.55 mm, and the spacing S between adjacent patches was 0.15 mm. The 9×9 patch arraywas selected to maximum aperture efficiency; although, high gain enhancement could have been achieved using an 11×11 or 13×13 path array. The 9×9 patch arraydefined an area with a side length of 6.15 mm.

4 FIG. 5 FIG. 4 FIG. 5 FIG. 100 118 112 100 100 118 As shown in the graph of, the antennaenhanced the gain of the waveguide probe antenna from a baseline of 6.5 dBi for the reference antenna to 20.1 dBi. It should be noted that, while the antenna was configured to enhance gain in the frequency range of 150 GHz to 170 GHz, the same enhanced gain (as well as other properties measured herein) can be achieved at any frequency by adjusting the dimensions of the patchesand patch arrayfor the desired frequency range. That is, the properties of the disclosed antennaare scalable.provides a graph of the reflection coefficient as a function of frequency for the designed antennawith patchesof materials with different conductivity. From these graphs, it can be seen that the material with the highest conductivity (copper) performed the best in terms of maximum realized gain () and minimum reflection coefficient (). However, surprisingly and unexpectedly, the decrease in such properties for the lowest conductivity material (ITO) was relatively minor despite the ˜60× lower conductivity. In particular, the difference in maximum realized gain was 0.78 dBi, and the difference in minimum reflection coefficient was at most 0.5 dB across the frequency spectrum.

6 7 FIGS.and Further, to quantify the effect of conductivity on the antenna gain and efficiency performance, the conductivity of the material of the patches of the patch array with respect to copper was varied, ranging from bulk copper conductivity to 0.01% of copper conductivity.graphically depict the effect of material conductivity on the peak gain and radiation efficiency. For ITO, the peak gain and radiation efficiency drop is limited to 0.8 dBi and 11%, respectively, as compared to copper.

Table 1 provides a summary of the gain enhancement and radiation efficiency of the antennas having the patches of different materials and associated conductivities.

TABLE 1 Summary of Antenna Properties for Various Materials Copper Aluminum Bronze ITO Conductivity (S/m) 7 5.8 × 10 7 3.8 × 10 7 1 × 10 6 1 × 10 Peak Realized Gain (dBi) 20.14 20.1 19.92 19.38 Radiation Efficiency (%) 94 94 91 83

112 100 6 7 FIGS.and The analysis, as summarized in Table 1, demonstrates that a relatively low conductivity ITO can be used to provide a transparent patch arrayin a Fabry-Perot cavity type antennawith minimal loss in the antenna performance. As mentioned above, the ability to use lower conductivity materials broadens not only the scope of materials that can be used but also the deposition techniques available for the fabrication of such antennas. It should be appreciated that Table 1 is intended to be more specific, indicating properties at specific conductivities, whereasare intended to be more general, illustrating general trends in peak gain and radiation efficiency for a range of conductivities.

8 FIG. 112 shows the gain enhancement comparison using copper and ITO as the material of the patch arraywith the source antenna as reference. Gain enhancement in ITO was about 13 dB as compared to about 13.8 dB in copper. Again, this result demonstrates that there is minimal diminishment in terms of antenna performance when using the low conductivity ITO material in place of the copper.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein, the article “a” is intended to include one or more than one component or element, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.